VansAirForceForums  
Home > VansAirForceForums

-POSTING RULES
-Advertise in here!
- Today's Posts | Insert Pics

Keep VAF Going
w/a Donation






VAF on Twitter:
@VansAirForceNet

  #1  
Old 05-13-2023, 09:47 PM
seagull seagull is offline
 
Join Date: Dec 2019
Location: Highland, CA
Posts: 615
Default venting of the fuel tank

My -12 is 2015 model with the fuel tank to one side.
A couple of days ago I put 19 gallons in my tank when the hangar was at 60f. Today the hangar is 95f and I opened the filler cap, sealed type, and heard a "pop" like air going out. I thought it was strange since the tank is vented.

To test it I put an air compressor hose into the filler neck sealed with a rag and gave a shot of compressed shop air. Fuel immediately came out of the overflow on the bottom of the fuselage.

I'm thinking about how the plumbing is done with the air vent at the top of the tank this would make sense fuel would come out when the tank is under pressure until the fuel in the tank is below the air vent fitting. I could see that it is possible to loose fuel in a topped off tank this way.

Does anyone have a different setup?
__________________
Live as if you were to die tomorrow. Learn as if you were to live forever.
visit my blog - http://waltsrv12.com
-- Walt --
Reply With Quote
  #2  
Old 05-14-2023, 01:40 AM
PaulvS's Avatar
PaulvS PaulvS is offline
 
Join Date: Aug 2019
Location: Western Australia
Posts: 1,479
Default

Be careful pressurising a fuel tank with an air compressor as it can easily be damaged. It sounds like the tank was filled to the top, in which case I would expect fuel to come out the vent pipe as it expands or is expelled by being pressurised.
__________________
Paul vS (yes I'm also a Van)
Building RV-6A #22320 O-320 FP. Airframe structure 95% complete, now working on integration, plumbing and wiring.
Flying my Aeroprakt A-22 STOL and the aero club's RV-9A while I build
Reply With Quote
  #3  
Old 05-14-2023, 06:32 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 8,456
Default

If the vent routing is anything like the 6 or 7, vans routes the vent up about a foot above fuel level then back down. If that vent line gets fuel in it, the upper lift acts like a manometer and a small pressure will build in the tank if the cap seals well. The pressure produced is very small and won't harm anything.
__________________
N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
Reply With Quote
  #4  
Old 05-14-2023, 08:25 AM
seagull seagull is offline
 
Join Date: Dec 2019
Location: Highland, CA
Posts: 615
Default

Quote:
Originally Posted by PaulvS View Post
Be careful pressurising a fuel tank with an air compressor as it can easily be damaged. It sounds like the tank was filled to the top, in which case I would expect fuel to come out the vent pipe as it expands or is expelled by being pressurised.
I regulated the pressure to 5psi and did not hold it on, only a short burst.
__________________
Live as if you were to die tomorrow. Learn as if you were to live forever.
visit my blog - http://waltsrv12.com
-- Walt --
Reply With Quote
  #5  
Old 05-14-2023, 08:31 AM
seagull seagull is offline
 
Join Date: Dec 2019
Location: Highland, CA
Posts: 615
Default

Quote:
Originally Posted by lr172 View Post
If the vent routing is anything like the 6 or 7, vans routes the vent up about a foot above fuel level then back down. If that vent line gets fuel in it, the upper lift acts like a manometer and a small pressure will build in the tank if the cap seals well. The pressure produced is very small and won't harm anything.
The vent line exits the tank and rises to the top of the fuselage with a ďTĒ fitting that acts as an air break to prevent siphoning in case the line fills with gas.

I would think a vent placed at the highest point maybe in the filler neck would allow air to escape before fuel is pushed up the factory vent in the tank.

I realize the easy solution is donít top the tank but in the -12 the last gallon or two is good for 1/2 hour of flying.
__________________
Live as if you were to die tomorrow. Learn as if you were to live forever.
visit my blog - http://waltsrv12.com
-- Walt --
Reply With Quote
  #6  
Old 05-14-2023, 09:22 AM
Bob Y Bob Y is offline
 
Join Date: Jul 2017
Location: Piedmont, SC
Posts: 503
Default

Quote:
Originally Posted by seagull View Post
I would think a vent placed at the highest point maybe in the filler neck would allow air to escape before fuel is pushed up the factory vent in the tank.
Thatís exactly what Vanís did for the fuel-tank vent on the iS.
Attached Thumbnails
Click image for larger version

Name:	IMG_0965.jpeg
Views:	69
Size:	704.1 KB
ID:	42383  
__________________
Bob Y - builder 12iS
N569TT first flight 2/9/2020
#121047
Reply With Quote
  #7  
Old 05-14-2023, 10:15 AM
seagull seagull is offline
 
Join Date: Dec 2019
Location: Highland, CA
Posts: 615
Default

Are there any other vent lines on the iS?

I am considering capping off the tank vent and adding a vent to the filler neck. Removing the air break and running the new vent line out the bottom.

Can anyone think of a reason, besides the work involved, not to do this?
__________________
Live as if you were to die tomorrow. Learn as if you were to live forever.
visit my blog - http://waltsrv12.com
-- Walt --
Reply With Quote
  #8  
Old 05-14-2023, 11:06 AM
Bob Y Bob Y is offline
 
Join Date: Jul 2017
Location: Piedmont, SC
Posts: 503
Default

Nope; thatís the only one.
__________________
Bob Y - builder 12iS
N569TT first flight 2/9/2020
#121047
Reply With Quote
  #9  
Old 05-31-2023, 03:20 PM
Stuart Grant Stuart Grant is offline
 
Join Date: Mar 2023
Location: Miami, Florida
Posts: 22
Default Fuel Tank Vent Location

I recently installed the tank vent back to the tail cone in my legacy (2013) RV-12 still being assembled. In that setup Van's design ** has the vent (a hollow rivet like the static ports) placed directly behind the aluminum overflow tube so that it is (I assume) not in the air steam where there may be negative pressure. On Cessna's the tank vent is behind the strut cuff where the strut attaches to the wing. This is done (I assume) to block it from being in the air steam. Kitplanes magazine has articles on the complexities of fuel tank venting. Be careful.

**I followed the design shown on Drawing 37-08, Revision 3 Dated 12/29/13 and ordered the parts shown in the drawing. This revision came after my kit was shipped. I had to open the fuel tank for the service bulletin so I did other mods, the added vent port and the strainer inspection port. I will also do a vented fuel cap.

Last edited by Stuart Grant : 05-31-2023 at 05:42 PM. Reason: Added Info
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 05:12 PM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.